Tapered Beam-Column with non-prismatic elements for Electrical Transmission Structure Supports

ABSTRACT

This invention uses a hybrid of latticed steel and tapered tubular steel technologies. Namely, latticed steel and tapered tubular steel pole technology, to provide a more economical structural support with the advantages of each. It utilizes latticed steel hot-rolled angles for bracing elements and cold formed steel plate for main leg elements. The tapered geometry of the leg elements provides a more optimum utilization of material by the use of a non-prismatic (tapered) element profile. This element consists of a bent plate shape profile that varies in structural section modulus vertically along the height of the structure which optimizes the use of steel material to resist the applied structural loads. The arms include an invention that allows for post-tensioning and thereby provides deflection control and/or the ability to modify the natural frequencies of vibration to mitigate vortex induced vibrations caused by wind. The main support elements in the arms are developed using plates formed into angle shapes that provide inherent gusset plate material to accommodate the bracing bolted connections without the need for separate gusset plates. The direct embedded portion of the structural design allows for transverse passive soil pressures to be collected by trapezoidal plates and resisted by the grillage superstructure. A transition section is subpart of the embedded structure portion and accommodates multiple structure heights as a standard foundation system.

CROSS REFERENCE TO RELATED APPLICATIONS

U.S. Pat. No. 5,079,891 January 1992 Paris U.S. Pat. No. 4,646,505 March 1987 Paris U.S. Pat. No. 3,942,296 March 1976 Edwin U.S. Pat. No. 2,284,898 June 1942 Hartman U.S. Pat. No. 1,880,000 August 1932 Wallen U.S. Pat. No. 1,762,112 May 1928 White

BACKGROUND OF INVENTION

Latticed tower supports have been used since the early 1900's to support medium and high electrical power transmission circuits. These latticed steel works are traditionally made using hot rolled steel angle shapes, positioned geometrically into topology that utilizes truss action to optimally provide structural support of the conductors and shield wires needed for electrical power transmission. The word ‘optimally’ or ‘optimized’ used herein refers to the minimization of material and/or material cost associated with the design, fabrication and supply of said structure supports. During the 1970's and 1980's a new steel support structure was developed using plate steel cold formed into tapered tubular shafts commonly referred to as tubular steel poles that support these electrical circuits. These tubular steel pole supports and latticed steel tower supports are the most common types of supports for operating voltages of 69 kV (kilovolts) and above, which is considered high and ultra-high voltage operating voltages.

Today, most new high voltage transmission lines are designed and constructed using either latticed steel or tubular steel poles for structural support depending on the economies and land restrictions in transmission line rights of way. Wood pole, concrete and fiber-reinforced polymer pole supports are also used, but to a lesser extent at these operating voltages.

SUMMARY OF THE INVENTION

This invention uses a hybrid of both technologies. Namely, latticed steel and tapered tubular steel pole technology, to provide a more economical structural support with the advantages of each. The invention has the general shape of a tubular steel pole, but utilizes latticed steel structural support elements. The invention utilizes latticed steel hot-rolled angles for bracing elements and cold formed steel plate for main leg elements. The nearly vertical main leg elements also provide a more optimum utilization of material by the use of a tapered member (non-prismatic) profile steel element. This element is a ninety-degree bent plate (or sixty-degree in the case of triangular shaped topology) that varies in width from the base of the structure located at the ground line to the first arm connection, waist, or other point along the vertical axis. This use of bent plate, with various constant plate thicknesses, places structural stiffness and steel area where it is needed to resist the structural loads. The main support elements in the arms are developed using cut plate patterns that provide integral gusset plate material to accommodate the bracing connections without the need for separate gusset plates increasing weight, cost and structural connection complexity.

All of the elements are connected by bolted connections, which provide simplicity and a more economical fabrication process as opposed to welded connections for tubular steel pole fabrication. Bracing elements along the vertical structure have varying incidence angles with respect to the main leg member. This allows for efficiencies in fabrication by selectively varying the bracing member length and respective angle of inclination such that an identical sized and detailed bracing member is used in multiple locations along the vertical structure length. In addition, the need for a base plate structural element at the pole base is negated due to the latticed steel geometry and use of main leg elements that directly transfer the load reactions into the foundation system. This foundation system can either consist of stub angles embedded in a reinforced concrete drilled pier caisson foundation or stub bent plate or hot-rolled angles transitioning to a grillage-type foundation directly embedded into the soil. In structural engineering terminology, the type of structural support system is a tapered non-prismatic beam-column with dominant loading resulting from transverse extreme wind or longitudinal conductor tension loads applied parallel to the global horizontal direction. The invention also includes a direct tensioner (post-tension element) in the structure arms to be used to maintain arm deflection under structural load or to adjust arm deflection after the construction process of stringing and sagging the conductor tensions or to provide structural detuning capability to counteract any vortex induced vibration due to wind producing fatigue loading. Finally, the invention includes a grillage foundation option to utilize a direct embedded foundation that is internally compactable with select backfill providing a cost effective, highly reliable foundation system. These concepts have been developed and are presented herein using electrical clearances and structural loading utilizing a typical 138 kV suspension transmission circuit although the same concepts utilized in this invention can be scaled for higher (or lower) electrical operating voltages and differing structural topologies. Electrical voltages only effect the clearances (distance from high voltage potential to ground potential) required for the structural topology. Single circuit, double circuit or single-phase support configurations can be utilized at either suspension, running angle suspension or line termination functionality. In addition, either self-supporting or guyed supporting configurations can be utilized with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of the invention and specific locations are shown in the set of Figures defined below as:

FIG. 1. an overall profile view from the longitudinal direction;

FIG. 2. an oblique view showing the structure arms and adjustable post-tensioning mechanism;

FIG. 3. an oblique view of the mast section showing the non-prismatic leg elements and associated staggered bracing elements.

FIG. 3a . a single shape made from bent plate, non-prismatic.

FIG. 3b . a combined bent plate shape into structure geometry, non-prismatic.

FIG. 4. Arm tensioner or de-tuner.

FIG. 5. An Integral Gusset plate showing how weight is reduced by avoiding overlapped plate.

FIG. 5a . Traditional gusset plate application for the arm of FIG. 5.

FIG. 6. an oblique view of the grillage foundation system with components.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-6, the invention uses a tapered mast topology of latticed steel elements with non-prismatic elements for the main load resisting elements. The use of latticed steel in a pole-type configuration allows for better optimization of steel material and the use of the non-prismatic elements provides an eight fold increase on the possible design permutations for the design process and selection of member sizes as compared to hot-rolled angles currently available in the marketplace, increasing the amount and degree of structural optimization. As a truss (FIG. 1) the structure has inherent structural benefits of reduced weight as compared to tapered tubular steel poles commonly used in the electrical transmission industry which transfer loads through plate shear action on multi-sided cold formed plate geometries. Trusses have been utilized in structures since the 1920's and typically consist of commercially available hot-rolled steel angle shapes. However, historical topologies have consisted of commercially available prismatic shapes arranged in structural geometries that depend on relatively large-scale (i.e. large footprint, or large area at ground level) truss action by which definition consists of a two-force element (compression or tension) with consistent force and resistance from individual element support node to element support node. Allowing for non-prismatic individual member section thickness and shape, the historical limitations on typical truss geometries are expanded to include narrow based structures, similar to a tapered tubular steel multi-sided or round pole. The bracing geometry produce a higher level of optimization opportunity reducing steel material weight and cost. The non-prismatic main leg structural support elements (FIG. 2:Item 1, FIG. 3, 3 a,3 b) resist both axial and bending stress (with P-delta amplification), the proportions of which depend of the structure topology, bracing geometry, and load magnitude. These non-prismatic main leg elements are cold bent plate formed from a flat trapezoidal-like shape, typically bent ninety degrees with bending radii limits according to industry standards to avoid significant strain hardening. Shape geometry is dependent on structural load demand. Typically, one single shape profile is utilized for each main leg element (FIG. 3a ), however multiple shaped profiles can be combined (FIG. 3b ) to create additional load resistance capacity depending on the load demand and positioned into various structural geometries and final topologies.

The bracing elements (FIG. 2:Item 2, FIG. 3) are positioned such that optimal truss action is assured negating the need to provide high bending stress resistance relative to axial resistance and are successively positioned geometrically to use identical bracing element length geometry along each mast section creating fabrication economies of scale. This is accomplished by varying the angle of incidence of the bracing element with respect to the main leg element being braced along the height of the structure. The unsupported length of the main leg elements varies according to the position of the successive bracing elements. This process of geometric positioning creates equal length bracing elements and the unsupported main leg elements are structurally controlled by the steel yield strength for these short elements due to their relatively low slenderness. Structural bracing can either be standard coincident bracing whereby out-of-plane brace point nodes coincide with in-plane brace point nodes for highly loaded structures (line termination), or the bracing can be staggered which provides benefits of positioning and detailing (locating and describing the connection holes) of assembly by avoiding bracing element conflicts for lighter loaded structures (tangent suspension).

The arms (FIG. 2:Items 3,4,5, FIG. 4) utilize an adjustable post-tensioning device that is used to counteract the defection at the end of the arm, and by detuning the arm to mitigate wind vortices that may cause aeolian or vortex-induced-vibration (VIV) producing fatigue loading. Adjustments are made at the central control rod (at arm bend) to control the geometric positioning of two sets of tension hanger elements that are adjustable byway of moving their relative positions along a threaded rod and thereby decreasing (or increasing) their lengths thereby increasing (or decreasing) their tensions which modify their structural natural frequencies of vibration and eigenvalues (mode shapes). This adjustment is made by moving the end positions along a threaded rod (control rod) on the top of the arm that spans the width of the arm. The relative movements of the end positions of the upper hanger elements (located outside the inboard arm portion connected to the structure mast) with respect to the lower hanger element (located inside the outboard arm portion connected to arm end) allow this tension change to take place. These tension hanger elements are positioned such that maintenance adjustments can be made after the line is strung (post-tensioning) or while the transmission line circuit remains energized avoiding the need to de-energize the power line for these adjustments.

An integrated gusset plate as shown in FIG. 5 is invented to avoid the need to use separate gusset plate material in connections that require multiple bolted connections that cannot fit into the dimensional constraints of the element being connected. The gusset functionality is integrated into a bent plate element that utilizes the main load resisting element of the structure subcomponent. The process creates a dual purpose for the main load resisting element. One; a primary purpose to resist the forces in the element, and two; a secondary purpose to allow for the connection of bracing elements to increase its load carrying capacity. Traditional use of gusset plates, as indicated in FIG. 5a , are avoided, reducing structure weight and lowering manufacturing, material handling, and on-site construction cost.

A grillage foundation system is invented (FIG. 6) that uses an engineered structure of bent plate elements, bracing elements and trapezoidal plate elements directly buried into the soil to resist the loading from the tapered lattice structure. The invention uses the concept of standardization to implement the concept for multiple height structures as what are often used in an electrical transmission line. The grillage foundation system connects the base of the tapered lattice structure defined above to a transition segment by way of a butt splice connection. The transition segment is a truss segment that changes (or transitions) the shape of the foundation to a straight truss section that extends to the length required for the embedment based on the structural load demand, soil type and in-situ soil condition. The trapezoidal or corrugated plate, place on alternating bracing panel segments are provided to resist the passive soil pressures exerted from the foundation system onto the surrounding soil and soil backfill. The transverse and longitudinal dimensions of the straight embedded portion of the foundation are consistent for all structure heights. The length of the straight embedded segment varies according to the height of the above ground structure, structural load demand, and soil type. Each unique structure height requires a unique transition section to match the geometry of the above ground structure with that of the straight embedded foundation. The transition section provides the adjustment needed for multi-height structure topology and minimizes the use and cost of steel material by standardizing the foundation system to a single dimension that only varies in embedment depth, also standardizing the size of the hole auger equipment required for installation, thereby saving cost over the length of a typical transmission line. These comparisons are comparing the grillage foundation system with that of a tapered tubular steel pole, which is also can be embedded. Additional cost savings are achieved by the ability to compact the soil backfill both inside and outside the grillage foundation, thereby providing structural support to the outside bearing surfaces and increasing its load resistance capacity.

The above descriptions should not be considered as limitations on the scope of the invention. Many other structural topologies are possible. Accordingly, the scope of the invention is determined by the claims and their legal equivalents. 

1. A method of using cold-formed non-prismatic steel plate for leg and main load carrying elements in a structural support for electrical power transmission structures. Utilizing these elements, structural resistance can be more optimally provided minimizing structure weight and associated cost. Load resistance is provided with variable section modulus with increased height taking advantage of tapered topology, and non-prismatic shape geometry reducing weight and cost.
 2. A method of using hot rolled or cold-formed steel angle elements as bracing elements in a topology that optimizes structure weight and fabrication. By positioning successive structural elements with inclination angles varying along the tapered geometry of the mast, identical length elements are achieved minimizing fabrication costs for high volume fabrication. End connections are identical and variations to necessitate consistent multiple end bolt spacing is accommodated with gage line variations on the main leg of claim
 1. Said bracing is utilized in a single or in a cross brace configuration depending on load demand. Said bracing is either standard bracing, collocated at nodal points for all bracing planes, or for staggered bracing whereby out-of-plane bracing points lie at non-coincident locations.
 3. A method of adjusting the deflection, and/or structural natural frequencies and mode shapes of the loaded or unloaded arm, the post-tension adjustment allows for pre-load or post-load adjustments to counteract vertical deflection or to counteract aeolian or vortex-induced-vibration (VIV). By way of adjusting the relative positions of the tension elements along an arm configuration, the lengths of the tension elements are reduced or increased allowing for vertical movements at the end of the arm where the insulators are attached and changes in the natural frequencies and mode shapes associated with the arm. When the upper tension elements are translated inward, along their threaded rod, and the lower internal tension elements are translated outward, along their threaded rod, the length from the upper arm connection to end of the arm is reduced, moving the arm vertically positive (up) and changing its natural frequencies and dominant modes of vibration.
 4. A method of providing optimum weight by integration of gusset plate functionality into the steel elements of claim
 1. By providing for additional steel plate material where it is needed, that is an integral part of the main load-carrying element, multiple bolt connections that are typically required for load transfer at truss bracing points are integrally provided by the main load-carrying element.
 5. A method of using structural steel elements as a system of structure support identified in claim 1 and claim 2 for resisting the reactions using a combination of steel angles with bracing elements and trapezoidal plate elements whereby transverse passive soil pressures are collected by the trapezoidal plates and resisted by the grillage superstructure. A transition section is part of the embedded structure portion and accommodates multiple structure heights as a standard foundation. Construction access is available for backfill compaction exteriorly and interiorly and this increases the foundation capacity as compared to direct embedded tubular steel poles. 